\begin{table}[htbp]\centering
\def\sym#1{\ifmmode^{#1}\else\(^{#1}\)\fi}
\caption{Electoral System, Candidate Communication, and Change in Partisan Affect (Traits)\label{tab:apt}}
\begin{tabular}{l*{3}{c}}
\hline\hline
                &\multicolumn{1}{c}{(1)}   &\multicolumn{1}{c}{(2)}   &\multicolumn{1}{c}{(3)}   \\
                &Affective Polarization   & In-Group   &Out-Group   \\
                &     b/se   &     b/se   &     b/se   \\
\hline
RCV Compliment  &    0.003   &    0.005   &   -0.002   \\
                &  (0.003)   &  (0.004)   &  (0.005)   \\
RCV Comp. + Endorse&   -0.000   &   -0.001   &   -0.000   \\
                &  (0.003)   &  (0.004)   &  (0.005)   \\
Constant        &   -0.015***&   -0.002   &    0.028***\\
                &  (0.002)   &  (0.003)   &  (0.003)   \\
\hline
R$^2$           &     0.00   &     0.00   &     0.00   \\
\textit{N}      &     2250   &     2250   &     2250   \\
\hline\hline
\end{tabular}
\end{table}
